<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .parent {
      position: fixed;
      left: 100px;
      height: 300px;
      width: 600px;
      background-color: pink
    }

    .son {
      position: fixed;
      top: 100px;
      left: 5px;
    }
  </style>
</head>

<body>
  <div class="parent">
    123
    <div class="son">
      23423
    </div>

</body>

<!-- <script>

  // var a = 10;
  function a() {
    console.log(456)
  }
  (function () {
    if (false) {

      function a() {
        console.log(123)
      }
    }
    console.log(a);  // 这个打印结果是要看浏览器的
    a()
  })()

</script> -->

</html>